Most modern transport aircraft, particularly those operating in the high subsonic or transonic range have sweptback wings and include numerous aerodynamic control surfaces. These control surfaces include inboard and outboard ailerons, trailing edge flaps, front opening slaps and spoilers located on the aft portion of the wing in front of the trailing edge flaps. As is well known, the ailerons are used for roll control. The rear mounted flaps and front opening slats are used to increase lift at landing and takeoff. The rear mounted spoilers typically are used to decrease the lift of the air foil during descent. On some aircraft they are used for roll control and during landing they become speed breaks in that they are raised to an almost vertical position. Typically, these control surfaces can provide sufficient aerodynamic control for the entire flight envelope of the aircraft, including takeoff, climb, cruise, maneuvering, descent and landing.
But during certain high speed maneuvers an unusual problem occurs on large wide bodied aircraft which have had their gross weight increased and are flying at higher than normal altitudes. During these maneuvers the outboard portion of the wing can become stalled. Since these aircraft have sweptback wings, the outboard portion of the wing is behind the center of gravity of the aircraft, whereas the inboard portion of the wing is in front of the center of gravity. Thus, if the outboard portion tends to stall, lift is still being produced at the inboard portion in front of the center of gravity and the aircraft tends to pitch up. In the past the approach taken to eliminate this pitch up condition in this particular portion of the flight envelope has been to program into the electronics of the control system movement of the existing control surfaces to dampen out the pitch up or eliminating that portion of the flight envelope altogether. But the complexities of the flight control system are dramatically increased, thus, alternate solutions have been sought. Applicant's solution is to provide a spoiler system to be mounted essentially on the rear portion of the front opening slat which will increase drag and reduce lift on the inboard portion of the wing when extended.
The concept of a front opening slat with a front mounted spoiler is not new. For example, U.S. Pat. No. 2,070,006, "Wing Spoiler," by B. G. Eton, Jr., et al, discloses a front opening slat which is mounted over a leading edge spoiler. The spoiler is mechanically coupled to the ailerons which are both raised simultaneously to spoil lift over the airfoil during landing conditions. This disadvantage of this system is that it cannot be used during high speed flight because the front opening slat must be extended prior to the extension of the front mounted spoiler.
Another example of front mounted spoiler is found in U.S. Pat. No. 2,719,014, "High Lift Airplane With All Moving Tail Unit," by O. C. Koppen. Here the same problem exists, for the spoiler cannot be raised unless the front opening slat is extended.
Other patents of interest are: U.S. Pat. No. 2,631,794, "Air Foil Nose Flap Arrangement," by D. K. Warner; U.S. Pat. No. 4,120,470, "Efficient Trailing Edge System for an Aircraft Wing," by P. C. Whitner (a typical example of a rear mounted spoiler).
In the prior art references, the disadvantage is not only the fact that the spoilers cannot be extended unless the leading edge slat is extended, but also in the fact that their installation on the wing takes up considerable space and furthermore complicates the design of the wing.
Therefore, the primary object of the subject invention to provide a spoiler system for mounting on or near the leading edge of an airfoil.
It is another object of the subject invention to provide a front mounted spoiler which can be easily retrofitted to an existing aircraft.
It is a further object of the subject invention to provide a front mounted spoiler that is integral with the leading edge slat of the aircraft.